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Post by mmartell on Jan 20, 2022 17:14:20 GMT -5
I'm a little confused. Are you trying to see if the cpu is sinking the 3.3v ?
The reason for FLAGS0 bouncing around is the mcu resetting the dsp several times before deciding it's not working and throwing a DSP error. This I can prove with a scope probe on Reset and one on FLAGS0.
The resistor is an 0201 if I didn't have a microscope it wouldn't be visible.
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Post by mastertech on Jan 20, 2022 17:24:24 GMT -5
If you believe the DSP is causing the error then we do not need to go any further.
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Post by mmartell on Jan 20, 2022 18:37:57 GMT -5
I believe like you it's more likely the DSP than the mcu but I don't KNOW it any more than you do.
Is the test designed to see if the mcu will pull down the 3.3v rail supplied to it on the FLAGS0 line ?
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Post by mastertech on Jan 20, 2022 18:50:49 GMT -5
My thoughts were that if it did pull it down then it could be the MCU. If it did not pull it down then the DSP FLAG0 voltage might be failing. Plus to see if the error code would go to normal.
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Post by mastertech on Jan 20, 2022 18:59:22 GMT -5
If you do try this and you have to use a different resistor, up the ohm rating if possible.
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Post by mmartell on Jan 20, 2022 19:22:26 GMT -5
The posts on this site are not numbered but shouldn't this bother us ? repairalmostanything.com/post/15635There is voltage on the FLAGS0 pin in standby. There is no voltage present on the ic itself. There also is no voltage on this pin at the mcu with R7923 removed. I've measured the same voltage at some other pins on the DSP and some go to other ic's which also have no standby power. Not done tracing it out yet but there is some standby power leaking into this part of the circuit. |
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Post by mastertech on Jan 20, 2022 19:57:44 GMT -5
Here's what I have so far... 1.1v and 3.3v verified at the DSP. With R7923 removed I now have 0v at the mcu in standby and on. At TP1 I have 1.35v in standby and 3.3v when powered on. (  ?) Diagnostics now indicate FIRM ERROR with ^DSP 00.00 and ALSO ^GUI 00.00 ! ( ?) Have not yet removed the other resistors let me know first if you think this indicates something as I have a few things to take care of before I can get back to this. Think of R7924 as a drain in your sink. Many logic lines, when working with swinging voltages need to drain off the voltage quickly for the next cycle. Otherwise there could be residual voltage left on the line. So when R7923 was removed, the DSP FLAG0 line had no drain. So even when supply voltages were gone, that line still had residual voltage on it. Cpu still had a drain. I am sure you have more questions so fire away. |
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Post by mmartell on Jan 20, 2022 20:08:50 GMT -5
Makes sense. I won't be able to run that test tonight for sure but probably tomorrow. So use a 100 ohm resistor or how much ?
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Post by mastertech on Jan 20, 2022 20:25:38 GMT -5
Im thinking try 1k.
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Post by mmartell on Jan 21, 2022 11:23:10 GMT -5
Ok so I'm running 3.3v through a 1k ohm resistor to the FLAGS0 pin of the mcu after removing R7923 but still having the drain resistor R7924 in play. Is that right ?
The resistor is under the board so will only be able to read the voltage at the mcu, is that also ok ?
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Post by mastertech on Jan 21, 2022 11:44:20 GMT -5
yes and yes
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Post by mmartell on Jan 21, 2022 16:00:23 GMT -5
I'm seeing 1.63v on the FLAGS0 pin at the mcu and the error changed to DSP ERROR 02.
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Post by mastertech on Jan 21, 2022 16:18:47 GMT -5
I am surprised it is that low. Where did you tap in for the 3.3v supply on the jumper wire? Can you check voltage on TP1 and TP2?
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Post by mmartell on Jan 21, 2022 16:39:18 GMT -5
I tapped at R7922 under the board to the side of R7923 (removed) that goes to the mcu.
TP1 2.6v
TP2 3.3v
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Post by mmartell on Jan 21, 2022 16:46:47 GMT -5
There's an internal pull down resistor on that pin not sure if that makes a difference...
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?)
